The fluorine-containing organophosphorus compound has a good effect on the improvement of solvent resistance, chemical resistance, mold releasability, friction-abrasion resistance, etc. and thus has been so far used as various kinds of additives, a mold releasing agent, etc. So far well known fluorine-containing organophosphorus compounds includes, for example, phosphoric acid ester series or phosphonic acid ester series having linear perfluoroalkyl groups, and their utilization as a base oil for lubricating oil or grease has been limited, because they have a poor compatibility with perfluoropolyether oil, trifluorochloroethylene polymer oil, etc.
Phosphonic acid ester series having perfluoropolyether groups and having one terminal group consisting of phosphonic acid ester RfRPO(OR′)2 has been so far proposed. The phosphonic acid ester series are soluble in fluorine-containing base oil and have a good lubricability, but fail to fully satisfy recently imposed more stringent requirements for lubricability or rust preventiveness.
Patent Literature 1: JP-A-2003-27079
Phosphoric acid ester series having perfluoropolyether groups, or aryl phosphate, or phosphonate series, etc. having a mono- or poly-alkylene oxide bond group or not between the phosphorus and the fluorocarbon group have been also proposed. However, these compounds are liable to undergo hydrolysis, because the fluorine-containing group and the phosphoric acid group form a C—O—P bond, and thus have poor heat resistance and durability, failing to show a heat resistance, which is a characteristic inherent in fluoro series lubricating oil or grease.
Patent Literature 2: JP-A-6-136379
Patent Literature 3: JP-A-2002-510697